Not Applicable
Not Applicable
Not Applicable
The present invention relates to the operation of solenoid actuated devices, in particularly solenoid actuated valves, where it is desirable to have the flow through the valve proportional to the actuating current for the solenoid.
Proportionally operated solenoid valves have found widespread application in automotive engine controls where it is desired to have the engine computer control flow of fluid for engine control, as for example, in controlling the flow of fuel vapor from a storage canister into the engine inlet. In such applications precise control and linearity of response of the valve is necessary to maintain the fuel/air mixture for the engine to maintain fuel economy and control of emissions from engine combustion over a wide range of engine operating conditions of RPM and load.
In the operation of a solenoid operated valve, hysteresis is encountered between the flow through the valve responsive to a given solenoid current for increasing current and the flow through the valve for the same current level upon decreasing current. The amount of hysteresis although relatively small is significant in applications where precise flow control is required. Where the valve is employed for controlling flow of fuel vapor to the engine intake manifold, the deviations in flow through the solenoid operated valve experienced on increasing and decreasing current to the solenoid can result in improper combustion of the engine.
It has therefore long been desired to provide a way or means of minimizing the hysteresis effects of increasing and decreasing current flow in a solenoid where the solenoid is employed for the operation of a fluid flow control valve; and, this has been particularly desired for such a valve employed for the control of fuel vapor flow from a canister into an internal combustion engine inlet. It has further been desired to provide such a way or means of improving the linearity or proportionality of a solenoid operated valve in a manner which is easy to incorporate in the electronic engine controller and which is not prohibitively costly for high volume automotive production.
The present invention provides a method of controlling the flow of current to a solenoid operated valve in a manner which produces flow through the valve proportional to the solenoid current in a manner which minimizes or substantially eliminates the effect of hysteresis in controlling current between zero and maximum flow conditions for the valve. The present invention utilizes a set of target values of current for the desired flow through the valve which are established by calibrating the valve at various steady state values of current. During operation, as the current is changed in the valve for flow control purposes when it is desired to increase the flow through the valve, the current is first increased above the target value for the desired current for a relatively short duration of time and then decreased to the target value. Where it is desired to decrease the flow of the valve, the current is decreased for a relatively short duration of time below the desired target value for a short duration and then increased to the target value. The technique of the present invention has been found to reduce the hysteresis to a level which is not significant in the operation of the valve and provides flow through the valve which is substantially linear or proportional to the current flow in the valve from zero to maximum current flow through the solenoid for the range of currents encountered in service. The method of the present invention may be readily incorporated in an electronic controller for controlling current flow through the valve particularly for valves operated on a relatively low voltage such as that encountered in automotive applications and with no additional electrical or structural changes required of the valve.